Re: [AVT] Clock skew and RTP

[Dominique Fober <fober@grame.fr>]

Thanks a lot for your replies. It answers my question: resuming the thread, it appears that RTP provides a mean to detect the clock skew to NTP synchronized hosts via the SR RTCP packets, but don't include (itself or using a dedicated payload) an explicit solution.
In fact, I was not looking for a concrete solution but rather trying to clarify this point. An interesting thing in your feedback is also to get different points of view and practices concerning the problem (including contextual solutions). Additional feedback in this domain is welcome (if there is) and notably concerning video (may the problem be considered as equivalent in the audio and video domains).
df

>I would like to know if there is any mecanism and/or payload defined 
>to take account of the clock skew problem.  To be more explicit, here is 
>a brief description of what I mean by 'clock skew problem':
>
>Clocks on different stations are not running at the same frequency
>(we have commonly measured clock deviations up to 1 per 10000 ms).
>For real-time transmissions, it results in a problem similar to a 
>consumer / producer problem. 
>Let's take an example with a sender host A (the producer) and a receiver 
>host B (the consumer):
>if the consumer consumes the events faster than produced (the B clock is
>running faster than the A clock), it will unavoidably lack data in a 
>given delay,
>if the consumer consumes the events slower than produced, (the B clock is
>running slower than the A clock) it will unavoidably accummulate more and 
>more data, resulting sooner or later in storage capacity problems.
>
>Real-time streaming multimedia applications are generally buffering 
>up to several seconds of data in order to make up for the transport 
>latency variations. Therefore side effects of the clock skew aren't
>noticeable unless the transmission lasts several hours.
>
>What's the common way to solve this problem (if there is one) ? 
>are there any mecanism and/or payload defined in RTP ?
>
>----------------------------------------------
>Dominique Fober               <fober@grame.fr>
>----------------------------------------------
>GRAME - Centre National de Creation Musicale -
>9 rue du Garet  69001 Lyon France
>tel:+33 (0)4 720 737 06 fax:+33 (0)4 720 737 01
>http://www.grame.fr
>


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